1. Field of the Invention
The present invention relates generally to electrical plugs for electric appliances and, more particularly, to a rotatable electrical plug.
2. Description of the Related Art
The conventional electrical plug of the power cord of an electrical appliance is not rotatable relative to the power cord. When inserted into an electrical socket, the hard electrical plug is firmly held in place; however the flexible power cord may curve subject to external force. When using a portable electric appliance, for example, a vacuum cleaner, air dryer, electric hand tool or the like, the power cord may be stretched frequently, and the electric connection between the power cord and the electrical plug tends to be broken, resulting in a short circuit.
U.S. Pat. No. 5,399,093 and U.S. Pat. No. 5,775,921 both provide a rotatable electrical plug, in which a rotative connection is provided between the power cord and the prongs, so that the housing can be biased subject to the position change of the electric appliance after connection of the electrical plug to an electrical socket. According to these designs, a rotative coupling device with concentrically arranged annular contacts provides the rotative connection between the power cord and the prongs. The main drawback of these designs is the complicated connection structure between the power cord and the rotative coupling device. According to U.S. Pat. No. 5,399,093, annular conductors 52 are electrically connected to respective ones of the power cord conductors 48 via connection arms 80a, 80b, 80c which extend from annular conductors 52, each connection arm 80 terminating in a wire crimp 82a, 82b, 82c which attaches the respective connection arm to a respective power cord conductor 48. According to U.S. Pat. No. 5,775,921, connection tip 191 is provided at the annular metal cushion, and side openings 133, 134, 183 are respectively formed in the upright annular flanges 13, 18 for the passing of electric wires 21, 22, 23. The complicated structural design greatly increases the manufacturing cost of the electrical plug.
Further, the aforesaid two prior art designs use spring means (arcuate and linear spring contacts 54a, 54b, 54c in U.S. Pat. No. 5,399,093) to enhance the reliability of the connection between the power cord and the prongs. The spring means simply complicates the structure without providing any added function.
Therefore, it is desirable to provide a rotatable electrical plug that eliminates the aforesaid drawbacks.
It is the primary object of the present invention to provide a rotatable electrical plug, which prevents distortion of the power cord of the electric appliance, prolonging the service life of the product and ensuring the safety of the use of electric appliance.
It is another object of the present invention to provide a rotatable electrical plug, which has a simple structure and is inexpensive to manufacture, and easy to install.
To achieve these objects of the present invention the rotatable electrical plug comprises a housing having an inner cover shell, an outer cover shell abutted against the inner cover shell, a wire hole, an opening formed in the inner cover shell, and a substrate provided inside the outer cover shell. A rotary prong holder is mounted inside the housing and rotatably coupled to the opening in the inner cover shell. At least two prongs are respectively fastened to the rotary prong holder, the at least two prongs each having an outer side respectively extended out of the opening in the inner cover shell and an inner side respectively fastened to the rotary prong holder, the at least two prongs including one center prong and at least one side prong, the inner side of the center prong being fastened to a center of rotation of the rotary prong holder, the inner side of each of the at least one side prong being fastened to the rotary prong holder and spaced from the center of rotation of the rotary prong holder at a different distance. At least one annular contact member is respectively mounted on one side of the rotary prong holder opposite to the opening in the inner cover shell and concentrically arranged around the center of rotation of the rotary prong holder and respectively electrically connected to the at least one side prong. And at least two connecting members are respectively affixed to the substrate, the number of the at least two connecting member being equal to the number of the at least two prongs, the at least two connecting members each having a connecting portion for the connection of an electric wire and a contact portion respectively disposed in contact with the inner side of the center prong and the at least one annular contact member.
According to an alternate form of the present invention, the rotary electrical plug comprises a housing having an inner cover shell, an outer cover shell abutted against the inner cover shell, a wire hole, an opening formed in the inner cover shell, and a substrate provided inside the outer cover shell; a rotary prong holder mounted inside the housing and rotatably coupled to the opening in the inner cover shell; at least two prongs respectively fastened to the rotary prong holder, the at least two prongs each having an outer side respectively extended out of the opening in the inner cover shell and an inner side respectively fastened to the rotary prong holder and spaced from the center of rotation of the rotary prong holder at a different distance; a plurality of annular contact members respectively mounted on one side of the rotary prong holder opposite to the opening in the inner cover shell and concentrically arranged around the center of rotation of the rotary prong holder and respectively electrically connected to the at least two prongs, the number of the annular contact members being equal to the number of the at least two prongs; and a plurality of connecting members respectively affixed to the substrate, the number of the connecting members being equal to the number of the at least two prongs, the connecting members each having a connecting portion for the connection of an electric wire and a contact portion respectively disposed in contact with the contact members.